GOVERNMENT-commissioned research on fracking has been delayed until after the SNP conference, angering critics in the party who want to debate the controversial issue.

Ministers said last year that six expert reports on the safety and science of the gas extraction technology would be published by “summer 2016”.

The First Minister said last month they were due out “over the next few weeks", followed by a public consultation on fracking, which involves pumping pressurised water and chemicals into shale beds to release gas, something critics say risks pollution and worsens climate change.

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Now government sources have told the Herald the reports are not scheduled to appear this week or over the two-week Holyrood recess that runs until October 23.

That puts their publication beyond the SNP annual conference in mid-October, where there will be a debate on energy, as well as scope for topical resolutions.

The reports cover the impact of fracking on the economy, seismic activity, climate change, transport and decommissioning.

Health Protection Scotland is also carrying out a public health assessment.

It is understood a factor in the delay has been one of the experts being replaced.

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In July 2014, an Independent Expert Scientific Panel commissioned by the SNP government said hydraulic fracturing of shale gas would be possible, if challenging, in Scotland.

Amid growing calls for an all-out ban, ministers announced further research in January 2015.

This was followed by a moratorium on fracking and on underground coal gasification (UGC), which involves igniting underground coal beds to obtain gas.

However ministers refused to rule out fracking, and later lobbied to have the powers to tax it.

Ahead of last year’s autumn conference, at which the pro-fracking petrochemical giant Ineos paid thousands of pounds for a stall, SNP members worried about the party hierarchy’s intent founded Smaug, or SNP Members Against Unconventional Gas, to campaign for a total ban.

Delegates refused to support a ban, and party bosses then blocked a fresh debate this spring, ruling it was “not the role of conference” to mandate government on “specific policies”.

Holyrood narrowly backed a ban in June after the SNP abstained but the vote was not binding.

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Catherine Shea of Smaug said: “The delay is very disappointing. There was so much pressure on the Broad Alliance against fracking to produce work for this exercise and individuals and groups spent a lot of time on that. There will be a lot of disappointment it’s been deferred.”

Ministers will make a statement to parliament on Thursday about a separate review into UGC, but this is a parallel exercise to the fracking reports.

Green MSP Mark Ruskell said: “Communities across the central belt have been left in limbo. This delay is unacceptable. As we await a ministerial statement on UGC on Thursday, it’s essential the Scottish Government conclude their reports into other forms of unconventional gas extraction as soon as possible, and move towards a ban."

The SNP’s Holyrood manifesto said the party was “deeply sceptical” about fracking and said neither it or UGC would not take place unless it could be proven “beyond any doubt that there is no risk to health, communities or the environment”.

This set an extremely high bar to fracking, as scientific research deals in probabilities rather than absolutes such as “beyond any doubt” and “no risk” whatsoever.

Nicola Sturgeon subsequently rowed back on the commitment, saying it meant “a substantial risk” to the environment rather than a “negligible risk” like crossing the road.

The government said the reports would be published in full before a public consultation during winter 2016/17.